The present invention relates to improved ophthalmic lens elements and eyewear, including prescription lenses, spectacles, sunglasses, laser protective eyewear, and frames, coatings and edgings therefor.
Most conventional prescription lenses have relatively flat base curves. Such lenses provide a limited field of view due to peripheral distortion and/or physical size limitations. Their relatively flat shapes limit the amount of eye protection afforded by the lenses, particularly near the temples.
Wrap-around eyewear has been developed in an attempt to provide wider fields of view and greater eye protection. Wrap-around design also permits different and sometimes striking overall styles for the eyewear. However, wrap-around eyewear is typically non-prescription. These products also typically have flat base curves between 6 and 10 D. Wrap (and sometimes rake) are achieved by rotating and/or translating the optical axes of the lens in the as worn orientation. See e.g. U.S. Pat. No. 1,741,536 to Rayton; U.S. Pat. No. 5,689,323 to Houston et al. This causes the line of sight of the wearer to deviate from the optical axis, and optical performance is often significantly degraded. Peripheral vision is typically poor.
Early in the history of ophthalmic science, steeply curved prescription lenses had been described, although not as vehicles for providing greater field of view or eye protection. A relationship between curvature and through power is shown in the so-called xe2x80x9cTscherning""sxe2x80x9d ellipse. First described nearly 100 years ago, it attempts to identify combinations of lens curvature and lens power which have minimum abberation. The general form of the Tscherning ellipse is shown in FIG. 1. FIG. 1 is given for assumed typical values for lens parameters such as index of refraction, vertex distance, lens thickness, etc. The Tscherning ellipse retains its ellipsoid shape and inclined orientation for various assumed values of lens parameters, while the precise location of points on the ellipse may change. The ellipse of FIG. 1 is derived from the corrected von Rohr equation (after Morgan) solved for point-focal (zero astigmatism) distance vision.
The lower portion 10 of the ellipse is the so-called xe2x80x9cOstwalt sectionxe2x80x9d which describes a selection of relatively flat front surfaces for lens powers typically used in conventional prescription ophthalmic lenses. The upper portion 12 of the curve, called the xe2x80x9cWollaston sectionxe2x80x9d, describes much more steeply curved lenses which have never gained acceptance as lens forms, although there are historical instances of attempts to make such objects (e.g. Wollaston himself). See, M. Jalie, The Principles of Ophthalmic Lenses p. 464 (4th Ed. London, 1994). Because of difficulties in fabrication, such early lenses were probably of small aperture and, consequently, perhaps, regarded as unacceptable for cosmetic reasons and because of their limited field of view.
Modern lenses with steeply curved front spherical surfaces have been made for the treatment of aphakia (absence of the natural lens of the eye as in the case of surgical removal of the lens). The general form of these lenses is shown in FIG. 2. See M. Jalie at p. 151. Such lenses serve essentially as an eye lens replacement and are characterized by great thickness and high plus power (greater than +5 D and typically +12 D or greater). The aperture A of these lenses are of small size e.g. 26 or 28 mm in diameter. Typically such aphakic lenses have a plano radial flange 14.
Today, the vast majority of conventional prescription lenses are relatively flat, single vision, Ostwalt section, miniscus lenses which are glazed like window panes into flat outline spectacle frames.
Conventional Ostwalt section eyewear is sometimes covered, treated or coated to provide specific reflective or anti-reflective properties. Most familiar are sunglasses which provided with coatings for selectively blocking portions of the incident light spectra. Some such lenses are designed to create pleasing colors to an observer by selective selection or absorption of incident spectral wavelengths. Such coating may involve metallic mirror layers and/or stacks of vacuum evaporated or sputter coated metal oxides. For example, coating for sunglasses are disclosed in U.S. Pat. No. 2,758,510 to Axc3xcwxc3xa4rter. As another example, certain multi-layer antireflection coatings are disclosed in U.S. Pat. No. 4,070,097 to Geller. See also U.S. Pat. Nos. 5,719,705 and 5,959,518. Conventional Ostwalt section lens are also sometimes specially coated to protect the wearer from intense ultraviolet or infrared radiation, or from laser beams.
Applicants have studied the properties of steeply curved lenses and considered series of lenses having commonly prescribed plus or minus through powers. Applicants observed that such lenses could, in principle, provide a wide field of view and eye protection. However, certain problems would interfere with practical implementation of such wide-field lens. Generally there are problems of fabrication and distortion, and problems of producing a range of common plus or minus power prescriptions with or without available common astigmatism correction or xe2x80x9ccylxe2x80x9d prescriptions.
A more subtle problem is presented by the wide range of front surface powers which would be required to provide a range of common prescription powers. For the lens assumptions of FIG. 1, for example, the Wollaston section would be understood to teach a variation in front surface power of from about 15 D to about 20 D for a product line through-power range of from +5 D to xe2x88x928 D. This corresponds to a variation in radius of front surface curvature of from about 29 to about 39 mm, which represents a large variation in overall size and shape for lenses large enough to provide a wide field of view. Such lens cannot be fitted like panes into a single frame size, but, in fact, each prescription itself would dictate its own specialized frame size and style. While such unique styles have value, they are incompatible with providing mass-marketed eyewear with a consistent appearance.
A broad object of the present invention is to provide ophthalmic lenses with good vision properties.
It is another object of the present invention to provide a series of steep base curve lenses which are readily manufactured and dispensed.
It is another object of the present invention to provide an ophthalmic lens having good vision properties through a wide field of view.
It is another object of the present invention to provide a steeply curved lens with reduced distortion in peripheral regions.
It is another object of the present invention to provide eyewear which affords more effective eye protection.
It is another object of the present invention to provide steeply curved lenses in common power and astigmatism prescriptions.
It is another object of the present invention to provide eyewear for steeply curved prescription lenses with a consistent appearance and frame configurations for a range of prescriptions.
Certain additional advantages may be realized through the teachings of the present invention. The increased field of view allows the making of eyewear whose temporal edge is not visible to the wearer (apparent edgelessness). The teachings of the present invention also permit reduction of magnification effects and associated distortion in some steeply curved lenses.
Other advantages involve providing the eyewear designer with options heretofore unattainable in lens having good peripheral vision properties in various prescriptions. These include the ability to use smaller outline lenses, topologically and cosmetically interesting three-dimensionally curved lens edges and spectacle rims, and edge thicknesses and surfaces which are more readily hidden from view.
Other advantages involve the provision of novel sun lenses and protective eyewear tailored to provide certain desired cosmetic properties and certain reflectance and anti-reflectance properties.
These and other objects and advantages will be apparent from the following text and drawings.
Generally, the present invention relates to eyewear and ophthalmic lens elements therefor. Ophthalmic lens elements may include, according to context, finished or edged ophthalmic lenses, semi-finished lenses, lens blanks or molds therefor. Also included are wafers for forming laminated lenses or lens blanks
The present invention is exemplified with reference to FIG. 3 which illustrates some geometric aspects of the steeply curved, concentric lenses of the present invention. FIG. 3 shows a horizontal cross-section of left and right eyes (20 and 22 respectively). Each eye is shown having a centroid of rotation, 24 and 26. The centroid of rotation may be understood as a volume within the eyeball, having a diameter CD of roughly 1-2 mm, about which the eye appears to rotate as the direction of gaze varies. As shown in FIG. 3, left and right steeply curved lenses 28 and 30 are positioned about the eye. In the Figure, the optical axis of each lens is co-linear with the line of sight of each eye and represented by the lines 32 and 34 for each eye. These lines also represent the z axis of coordinate systems later used in the text to describe certain lens surfaces (the x-y plane being normal to the plane of the Figure).
The lenses 28 and 30 are generally describable as spherical or spherically based. In preferred embodiments, the front surface is spherical, having a fixed radius of less than 35 mm for all prescription values in the series. In other embodiments, the lens is best described as having a spherical back, as containing a reference sphere or as lying within a defined spherical shell. In each case the radius of the reference sphere or shell and the location of the lens as worn is such that the center of the reference sphere or shell lies close to or within the centroid of rotation of the eye. The case in which the front surface is a sphere of radius R centered on the centroid of rotation of the left eye is illustrated for the left eye in FIG. 3.
The selection of a spherical base of a given radius centered on or near the centroid of rotation of the eye, places a constraint on the vertex distance dv, illustrated for the left eye of FIG. 3 as the distance between the plane of the pupil 36 and the back surface 38 of the lens. Front surface radius and back surface shape, in conjunction with other design parameters such as the lens thickness and the index of refraction of the lens material determines the optical properties of the lens as described in detail below.
Applicants have found that the lens design of the present invention may be analyzed and described by a data array of a type illustrated in FIG. 4. The diagram is called a xe2x80x9cMorris-Sprattxe2x80x9d diagram after two of the inventors.
In the diagram, each dot is at the center of a theoretical ray-trace plot from a lens having properties of the grid point at the center of the dot. The xe2x80x9cyxe2x80x9d axis on the right gives the power of the front surface of the lens in diopters (normalized for an index of refraction of n=1.530). The xe2x80x9cxxe2x80x9d axis at the bottom shows the through power of the lens at its center. This corresponds to the plus or minus power prescription of the lens. For this Figure it is assumed that each lens is made of polycarbonate (n=1.586) and has a center thickness of 1.8 mm in minus power lenses, and a center thickness in plus lenses determined individually for each prescription so that the minimum overall lens thickness is 1 mm in the periphery of a 58 mm diameter lens blank. Each lens is positioned relative to the eye such that the front surface is 33.1 mm from the centroid of rotation of the eye, which is concentric for lenses which have a front surface power of 16.0 diopters.
At each individual grid point appears a ray trace result for eye rotation angles up to 40 degrees. The dark area at each grid point represents the region of each lens that has less than 0.125 diopters of RMS power error relative to the prescription and allowing up to 0.375 diopters of accommodation. RMS power error is defined mathematically below. This criterion is believed to be a good indicator of lens performance.
The fully filled-in circles in FIG. 4 represent lenses with less than 0.125 diopters of RMS power error over 40 degrees of eye rotation in any direction. For dots with rings around them, the RMS power error rises above 0.125 diopters for some intermediate eye rotation angles then drops below that threshold again for some small angular region.
The elliptical outline of the locally largest dots corresponds roughly to a Tcherning""s ellipse generated for the special case of the lens parameters selected by applicants. Conventional wisdom dictates that the front surfaces of spherical lenses (lenses with spherical surfaces on the front and back) must follow Tcherning""s ellipse to produce high quality lenses. However, the Morris-Spratt diagram illustrates that for appropriate selection of lens parameters there is a nearly horizontal region in this diagram where it is possible to produce excellent lenses. It is known that plano spherical lenses with high quality optics can be fabricated extending over a wide range of front surface curvatures (a fact that indicated by the vertical line of large dots near zero through power). Many such lenses are available in the market today. The novel idea that is illustrated in the Morris-Spratt diagram is that is it also possible through appropriate selection of lens parameters to fabricate high quality spherical lenses over a wide range of prescriptions using a single, steeply curved front surface or spherical reference surface or shell. Notice that the low RMS power error regions for lenses using a front surface power of 16 diopters (grid points on line 40) have wide angular extent (nearly full or full circles) over a range of at least xe2x88x926 to +4 diopters. Over 95% of all prescriptions fall within this range. Therefore, it is possible to produce high quality ophthalmic spherical lenses over a wide range of useful prescriptions using a single, appropriately selected high power front surface or base curve. Moreover, as made clear by FIG. 4, some small deviations from the single power or from exact concentricity may be made while providing good lens quality and a lens shape sufficiently consistent to use the same frame style.
FIG. 5 illustrates a series of good optical quality lenses of a preferred embodiment of the present invention. In this embodiment, the front surface is selected to be about 16 Dxc2x1about xc2xd D. This range lies between lines horizontal 50 and 52. Particularly preferred embodiments provide series of lenses having prescription in the range xe2x88x922 D to +2 D (area 54), xe2x88x926 D to +4 D (areas 54 and 56), or xe2x88x928 D to +5 D (areas 54, 56 and 58).
For comparison purposes, a portion of the Wollaston section of the Tscherning ellipse 60 for this special case has been overlaid on the diagram of FIG. 5. The Figure shows that the front curve and through power ranges represented in the horizontal blocks are inconsistent with the Tscherning ellipse teaching which would indicate a 5 D variation in the front surface for xe2x88x928 D to +5 D through power and a far steeper curvature in the center of the through power range.
Preferred embodiments of the present invention include series of lens elements defined by a single reference sphere concentric with the centroid of rotation of the eye of the wearer, where the sphere has a radius of curvature in the range of 25 to 50 mm, more preferably 30 to 35 mm and most preferably about 33 mmxc2x1about 1 mm.
Advantageously, the series of lens elements are provided with the appropriate prescribed power and cyl correction. In the embodiment where the front surface is spherical, the back surface is configured to provide the appropriate through power and cyl correction. In a preferred embodiment, a series of lens elements would include through power through the above-mentioned ranges in xc2xc D increments. Stock lens elements of each power would be provided with each of various common astigmatism prescriptions, for example, 0 D to xe2x88x922 D in xc2xc D increments. It will be understood that because of the spherical symmetry of the lens element, the angle of the cyl correction can be selected by appropriate rotation of the lens element during edging and glazing.
Conventional astigmatism correction is based on toroid surfaces often described in terms of principle meridia, i.e. orthogonal meridia centered at the optical axis of the lens, representing the locus of maximum and minimum curvatures. Barrel toroids and donut toroids have both been used to provide cyl corrections. As described below, applicants have developed novel astigmatism correcting surfaces for steeply curved lens, which surfaces can be described as lying between a barrel toroid and donut toroid each having the same principle meridia and the same power along the principle meridia. Two such surfaces are the xe2x80x9call-circular meridiaxe2x80x9d surface and the xe2x80x9caveraged-toroidsxe2x80x9d surface described in detail below.
The shape of lenses of the present invention will now be described. The term xe2x80x9csteep curvaturexe2x80x9d is used in this context to describe the overall shape of the lens or reference sphere or shell. In particular examples the curvature may be quantified as an average radius of curvature of a surface or of a spherical shell lying inside or outside the lens or containing a surface of the lens.
Lenses of the present invention are also characterized in general shape by their large angular field of view, often expressed as an angle between the optical axis and the temporal-most or nasal-most extremes of the edges. In accordance with preferred embodiments of the present invention, the lens subtends an angle centered on the center of a front spherical surface, the angle being greater than 80xc2x0 and in preferred embodiments greater than 100xc2x0. It will be understood that such angles are indications of the field of view of the lens provided of course that the lens is optically usable in these peripheral regions.
The unique topological shape of the lenses of the present invention may also be characterized by sagittal depth or xe2x80x9chollowxe2x80x9d depth, which are generally a measure of the three-dimensionality of the lens and lens edge. These depths relate to the distance between the fronto-parallel plane of the lens and the temporal most edge point, as described below. In accordance with preferred embodiments of the present invention, there are provided lenses with an average radius of no more than 50 mm centered on the centroid of rotation of the eye and having a hollow depth of at least 8 mm. In a particularly preferred embodiment the radius of the front surface is about 33 mmxc2x1about 1 mm and the hollow depth is at least 10 mm.
The present invention also includes methods for providing prescription eyewear. These methods employ lens elements having a steep curvature. Preferred embodiments employ a front surface which lies within a spherical shell of a thickness no greater than 2 mm and a radius of no more than 50 mm. A rear surface is formed in the lens element so that the lens element has a prescribed through power and a prescribed astigmatism correction. The lens element is positioned on the wearer so that the center of the spherical shell lies at or near the centroid of the eye by glazing into a frame having a standard aperture corresponding to a radius of a spherical shell common to a series of lens elements having different through power, including the prescribed through power. The eyewear provides the prescribed power and astigmatism correction through the wearer""s entire visual fixation field.
The present invention also includes specially designed spectacle frames. In a preferred embodiment the spectacle frame is suitable for use with a series of ophthalmic lenses, each having a spherical surface of a single radius between 25 and 35 mm, and a second surface selected to provide in conjunction with the spherical surface various common prescriptions. In preferred embodiments the frame is adapted to support left and right lenses on the wearer so that the centers of the spherical surfaces are located at or near the centroids of rotation of the left and right eyes, respectively. The spectacle frame may include temple pieces and rim portions for engaging the left and right lenses. The rim portion engaging each lens may be formed in the shape of a closed curve lying on a reference sphere having a radius approximately equal to the radius of said spherical surface. In such spectacle frames, the nasal-most point and temporal-most point of the closed curve may subtend an arc of greater than 90xc2x0 with a vertex at the center of the spherical surface.
The spectacle frames may include a left temple piece, a right temple piece and a nose bridge. In a preferred embodiment the nose bridge is of adjustable length to allow horizontal adjustment of the lens separation to position the centers of the spherical surfaces at the centroids of the eyes. In other embodiments, rimless frames are provided with novel fitments and hinges for supporting temple pieces, the hinges being adapted for direct attachment to the reference spherical surface at the temporal edges of the respective lens.
The present invention also includes novel lens edging which may be used with steeply curved lenses particularly those having at least one spherical surface with a radius of curvature between about 31 mm and 33 mm.
In such a case the lens may be edged so that an edge surface of the lens is approximately normal to the spherical surface of the lens. Eyewear made with such lenses may be rimless and the edge surface may be essentially invisible to the wearer because the edge surface lies approximately on the wearer""s line of sight when his gaze is cast in that direction. In addition, the appearance of the edge to an external observer is minimized. Such edge surfaces may be generated by a mill rotated about an axis which intersects the center of curvature of the spherical surface. In preferred embodiments, the edge surface is cut so that it subtends a small arc with respect to the center of curvature of the spherical surface where the arc lies in any plane which contains the optical axis of the lens.
The present invention also includes methods for making steeply curved lens elements adapted for mounting in eyewear. The method may involve molding a lens blank having a radius of curvature along a principle meridian of less than 35 mm over a substantial portion of its front surface. After molding a back surface is cut on the molded lens blank, which, together with the front surface, provides a non-zero prescription through power. Finally, the lens blank is edged to provide an edged lens having a maximum hollow depth of at least 8 mm. The cut back surface together with the front surface may be designed to provide a non-zero astigmatism correction for the wearer.
In one embodiment, progressive surface power addition is molded on the front of the lens blank. Alternatively, the progressive surface power addition may be incorporated in the back surface cut in the lens blank.
Other aspects of the present invention relate to steeply curved sun lenses such as the lenses with a spherical optical surface with a radius of curvature less than 35 mm described above. The suns lenses are made by coating and/or dying the steeply curved lenses of the present invention. In a preferred embodiment, an optical surface (for example the front surface) may be coated with a partially reflective dielectric stack which, in a particularly preferred embodiment, is generally blue in color. The surface coating may be a sputter-deposited multi-layer coating made up of alternating layers having relatively high and relatively low refractive indices. In particular the surface coating may be a stack of silicon and zirconium oxide layers, at least one of the zirconium oxide layers being greater than about 10 nm in thickness. The coating is designed so that its reflectance begins to decrease for incident light of a wavelength above about 480 nm and remains relatively low into the near infrared region.
The present invention also relates to protective eyewear including left and right lenses each having a spherical surface. Each spherical surface preferably has a radius of curvature between about 31 mm and 35 mm. Frames support the lenses on the face of the wearer so that the center of the spherical surface of each of the left and right lenses is located approximately on the centroid of rotation of the left and right eye, respectively.
Multilayer coatings may be formed on each lens for at least partially blocking transmission to the respective eye of radiation incident on the lens. The layers have selected refractive indices and thicknesses for at least partially blocking at least one selected portion of the spectrum of incident radiation. In sun lens embodiments, ultraviolet light may be at least partially blocked. Protection from laser radiation may also be provided by the eyewear in industrial or military settings. In this case coatings and/or dyes are provided to block laser light in a selected spectral range. In particular, infrared laser radiation may be at least partially blocked. Incident laser radiation is blocked sufficiently to reduce its power level to eye safe level. Off-axis incident radiation is blocked by the stack, absorbed by a dye and/or has an optical path which does not reach the retina.
In the protective eyewear embodiments of the present invention, advantageously each lens extends from the nasal margin of the orbital region to the temporal margin of the orbital region and from the lower to the upper margins of the orbital region, so as to stand between incoming radiation from all directions which would reach the retina, while affording the wearer a wide field of view.
The foregoing is intended only as a summary of the invention, the scope of the invention being determined by the literal language of the claims and equivalents thereof.